1. Technical Field
This disclosure generally relates to methods and apparatus for forming self-assembly arrays of substances, such as nanoparticles, on a substrate. In particular, this disclosure relates to the use of a micro-mold to control the dewetting dynamics of a liquid composition containing the substances and a solvent.
2. Description of the Related Art
Development of nanotechnology focusing on the control of matter on an atomic and molecular scale has gained significant interest in recent decades. In general, nanotechnology deals with structures having sizes of 100 nanometers or smaller, and involves developing materials or devices within that size. Nanotechnology is very diverse, ranging from novel extensions of conventional device physics, to completely new approaches based upon molecular self-assembly, to developing new materials with dimensions on a nanoscale.
Molecular self-assembly is an important aspect of bottom-up approaches to nanotechnology. Using molecular self-assembly the final (desired) structure is programmed in the shape and functional groups of the molecules. Self-assembly is referred to as a ‘bottom-up’ manufacturing technique in contrast to a ‘top-down’ technique such as lithography where the desired final structure is carved from a larger block of matter. In the speculative vision of molecular nanotechnology, microchips of the future might be made by molecular self-assembly.
Transition metal nanoparticles, such as gold nanoparticles, have been the focus of intense interest recently due to their potential use in the fields of optics, immunodiagnostics, and electronics. The transition metal nanoparticles may exist in a variety of shapes including spheres, rods, cubes, and caps. In application, the transition metal nanoparticles are generally coordinated to, and stabilized by, a ligand.
The development of parallel, inexpensive approaches to patterning crystalline materials is essential in making use of their outstanding properties in bottom-up nanodevices. Nanoparticle superlattices comprise a new class of crystals (‘supra-crystal’) with collective properties that are different from those of bulk phase materials, isolated nanoparticles and even disordered nanoparticle assemblies. For instance, coherent vibrational modes can only appear in highly ordered nanoparticle superlattices, and synergistic effects in superlattices can lead to enhanced p-type conductivity. Hence, nanoparticle superlattices are poised to become a ‘new periodic table’, which could be used for high performance devices such as high-density data storage, more efficient energy harvesting systems and ultra-sensitive biosensors.
Applying the collective properties of nanoparticle superlattice entities in nanodevices usually requires methods capable of patterning them into desired structures while maintaining a high degree of internal order. However, superlattices usually form from the evaporation of a drop of nanoparticle solution, which is essentially a far-from-equilibrium process. Capillary flow induced by a non-uniform evaporation field and fluid fluctuations during late-stage drying often lead to irregular features such as isolated islands, worm-like domains, ring-like structures and cellular networks. Owing to the statistical nature of drying-mediated self-assembly, it remains a challenge to pattern superlattices with comprehensive control over internal order and overall morphologies.